The present invention refers to a method for skinning tuna, bonito, swordfish, shark and other species used for the canning industry, its purpose is to make the removal of skin from these species highly automated, prior to the cutting up, dressing and canning of same. The invention also affects the device for the implementation of said method. Consequently, method and device are destined for the fish canning industry.
As it is known, fishing for tuna and the other aforementioned species and similar, is carried out in high seas from refrigerator vessels, where an initial preparation phase is carried out on the fish, ie; gutting and washing for them then to be immediately put into refrigerating chambers where they are kept for the fishing season, until the fish is eventually unloaded at the canning factory or factories.
Part of the initial phase of preparation of the fish is removing its skin, for which there are, at present, two methods:
Manual skinning, which requires considerable labour, and hence it is usual for tuna boats and similar to turn to underdeveloped countries where labour is very cheap for help in carrying the already skinned fish to the canning factory. This means, in addition to the labour costs, considerable travelling in many cases, with the subsequent costs and time involved in travelling, throughout which the expenses for maintaining the vessel and its crew are maintained.
The other solution is to directly transfer the fish to the canning factory and subject it to chemical treatment there, using products to remove the skin, in such a way that labour is drastically reduced and at the same time no additional travelling is necessary for the boat in looking for areas with cheap labour costs. However, the fundamental problem with this system is the negative effect that such products produce on the fish, substantially altering its flavour and achieving an end product that, for the consumer, is much less attractive than when hand-skinned, and all this without considering the fact that, often, the chemical products used for skinning can leave waste material on the flesh, which can, in turn, be harmful to the consumer.
The method proposed by the invention allows mechanical skinning, ie; skinning that produces a similar product to that which is obtained by the traditional manual skinning process, but with minimum labour, and, as a consequence, production costs that are considerably lower and the implementation of which takes place in the canning factory, although, whenever considered necessary, may take place on the fishing boat itself.
To this end and more specifically, this method is carried out in the following way:
The frozen fish is taken by its head and tail and is placed preferably vertically
Laterally to the fish and approximately corresponding with its mid section, a knife is placed on the surface of the fish at a certain angle and with certain elastic tension.
The fish is rotated on its imaginary axis
The knife is subjected to a tilting movement from one extremity of the fish to the other, with a parallel movement, in such a way that the knife is kept permanently on a level passing through the axis of the fish
The breadth of movement of the knife corresponds with the length of the fish, referring to the area of the fish to be skinned, in such a way that the combined movement of the knife, on the one hand, and of the fish on the other, generates a spiral action of the knife on the periphery of the fish affecting the entire surface of the fish.
When the skinning has been completed the movement of the fish is stopped, the knife is separated and the fish is taken from its fastening.
Given that, as mentioned previously, the skinning operation takes place when the fish is still frozen, there is the option of using hot water, steam, hot air or any other heat-producing method, that momentarily lessens the degree of freezing on the skin of the fish, in order to assist the knives"" cutting action.
The device planned for the implementation of the method is made up of a rotating turntable or is on a linear chain, on which one or more loading stations are set up, with their respective skinning stations, which in the first case, on the rotating turntable, will be diametrically opposite one another, and at each there will be two clamps to secure the fish, in vertical alignment, connected to a common rotating device and having the means to regulate the distance between them in order that this distance can be made to accommodate the different sizes of fish.
Said knife is placed laterally to the fish which will be in the shape of a glass, ie, cylindrical, hollow and open at its cutting edge, which will be placed to correspond with the imaginary opening of the glass, said edge or blade preferably having many internal facets or rabbets, half-moon shaped, equally distributed, very closely together, in order to achieve the best cutting conditions.
The shaft of the knife will be assembled with freedom of rotation on a supporting arm and aided by a motor transmitting a rotating movement of said knife on its own geometrical axis, said arm assembled to tilt on a support allowing the knife to move from one extremity of the fish to the other as it turns, as a result covering the entire surface thereof in a spiral cutting strip.
Said arm will also be permanently pressed against the body of the fish, by means of a spring or similar, so that the knife incise the latter with a level of penetration determined by a shoe or press which moves equally over the surface of the fish as it rotates.
As a complement to the described structure and given that the length of said supporting arm for the knife is invariable, in order for said knife to be effective at any point along the length of the body of the fish, the section and distance of which varies substantially in relation to the pivoting shaft of the arm, it is planned that the support of said arm should be assembled so that it can be moved transversally, activated, for example, using a cylinder or similar, so that the knife is nearer the fish corresponding with both extremities of same and is retracted as it reaches its mid section, specifically remaining on a plane passing through the axis of the fish, to which end, a sensor, also acting on the surface of the fish, continuously sends positional control signals from the knife to the cylinder causing the transversal movement of the support.
Both work stations set up on the rotating turntable can be identical, ie; both being supplied with the aforementioned cutting unit, in such a way that said cutting unit be inoperative in the loading station and operative in the skinning station, or said cutting unit may be set up in the skinning station exclusively.
In accordance with another preferred embodiment of the invention is the use of several skinning knives, working simultaneously, each one affecting a section of the body of the fish, so that, on the one hand, its mobility is considerably reduced and, on the other, the skinning speed is markedly increased.
It is also planned that the knives, instead of the aforementioned glass shape, be in a circular, serrated disc framed by a pair of turntables of a lesser diameter and with a perfectly smooth edge, which, when rotating with the knife itself, act like fences to the penetration of the latter in the body of the fish, and consequently having the means to set the depth of skinning.
Here, it is also planned that the different knives be attached to respective tilting arms assembled co-axially on the frame of the machine and activated simultaneously by a single engine, which transmits the movement of the knives through the hollow interior of the arms themselves, each of which is assisted by a twin effect pneumatic cylinder, which, on the one hand adequately presses the respective knife on the body of the fish during the skinning phase, and on the other, tilts the respective arm into a situation where it is inoperative, leaving the area where the fish is processed perfectly free for removing the skinned fish and substituting it for another.
It is also planned that each knife have a sluice-way, into which it throws the remains of skin taken from the fish, running into the different sluice-ways, at different heights, like the knives themselves, in a lateral, vertical and fixed collector which, in turn, runs into any suitable container underneath.
For this vertical movement of the knives along the length of the body of the fish, a bridge is set up on the frame of the machine, which is vertically mobile using a system of spindles and the respective motor, on the bridge are assembled the support arms for the knives and all their accessories.
Finally and for the purpose of fastening and moving the fish, the frame should have a rotating support at a low level, mounted on vertical guides and operated using a cylinder, said support having a lower motor that activates a clamp or flange with a pointed and serrated opening to be used to hold the head of the fish, vertically and with its tail pointing upwards, which is simply fitted inside a yoke-shaped support, able to rotate freely over the frame, in such a way that, because the lower rotating support can be moved at a height, it is very easy to implant the fish and it can be secured whatever its size, by lifting said lower rotating support to a greater or lesser degree, the upper yoke being slightly movable at a height because of the pressure exerted by the frozen fish at the final phase of fastening, in order to act on a sensor that keeps the knives inoperative until the fish has been correctly and definitively implanted into the machine.
For the rest, the machine will have electrical and pneumatic automated mechanisms so it may be operated correctly from a control panel.